This invention relates to a method and an associated device for obtaining access to internal organs, such as vascular components. More particularly, this invention relates to a method and an associated device for removing material internally from a patient. The method and the device are especially useful for removing clots from subcutaneous vascular bypasses or shunts.
Vascular bypasses, whether made of human tissue or polymeric material (graft), become regularly blocked with blood clots which must be removed. A common technique for cleaning clogged vascular bypasses is surgical: the skin surface and the underlying shunt are cut open and instruments are inserted through the openings to extract clumps of clotted blood.
The disadvantages of this conventional surgical procedure are well known. Because of the blood which naturally spurts out through the incision, the cleaning of the graft or bypass must be performed in the operating room. Of course, all the disadvantages or side-effects of surgery pertain: pain to the patient, danger of infection, loss of blood, as well as time and expense due to the requisite hospital staff.
Another common method of cleaning clogged vascular bypasses is dissolution of the clot via biological enzymes. The most common enzyme in current use is urokinase. The disadvantages of this method include high cost of the enzymes and a delay of as much as several hours while the enzyme acts on the clot. Systemic side effects of these enzymes, notably bleeding at other sites in the body due to unwanted yet uncontrolled dissolution of other "good" clots, are also seen.
Because of the limitations of surgical and enzymatic treatment, a myriad of other methods has been proposed to remove clot. The most intuitive method is clot removal via a suction catheter. Indeed this was first reported by Handley in 1907 in the British Medical Journal in a patient with clot at the bifurcation of the aorta. In his case report, a suction catheter was threaded upwards through a groin incision, but failed to remove significant amounts of clot. It was subsequently necessary to employ mechanical maceration and forcible saline irrigation in conjunction with the native aortic pressure to expel the clot and restore flow.
More recently, the use of suction thrombectomy has been reported in the medical literature, where large bore catheters (8-10 Fr.) are introduced and suction is applied to suck clot from the body. This technique has been revived by some vascular interventionalists as described in a few case reports. It has been used in areas where small amounts of clot can have critical consequences, such as the coronary arteries of the heart and pre-morbid patients with massive pulmonary embolism. Unfortunately, these catheters leave large and potentially damaging holes in the body. Furthermore, even these large catheters need to be repetitively removed and flushed secondary to adherent and obstructing clot. Bleeding from the resulting holes is also a major problem. This method has very limited applicability in clinical medicine and has largely been abandoned in favor of other methods.
Many mechanical devices known as "thrombectomy devices" have been described in United States patents. These patents are too numerous to review individually but the following general concepts apply to all.
Mechanical devices operate by many proposed mechanisms, including rotating catheter caps, drill bits and abrasive heads, high speed enclosed rotors creating a vortex which pulls in and macerates clot, wateijets based on various principles and with various configurations, ultrasonic devices, rotating wires baskets, brushes and blades, etc. Clot is macerated via these externally powered devices into a fine particulate size so that it may be aspirated through small device channels or be better tolerated if left in the body. In some devices, irrigation fluid is introduced to form a slurry of macerated clot and fluid or the patient's blood is used for this purpose. This approach of energized clot maceration has been thought by previous inventors to be the only possible rapid mechanical solution to the thrombectomy problem, considering the physical limitations of removing unmodified clot via suction through small diameter tubes.
Another general limitation of previously described devices is that clot is processed externally to the device and the blood vessel is used as a containment vessel. This permits clot particles to escape into the general circulation (embolization). In addition, biochemical aberrations in the blood secondary to microscopic red blood cell disruption (lysis) is routinely seen with some devices.
Recently, instrumentation has been described in U.S. Pat. No. 5,419,774 to Willard et al. to remove thrombus. This device has multiple lumens including two irrigation channels, a suction channel and a solid drive shaft all terminating in a common chamber distally where a reciprocating cutting mechanism is located. The device functions by sucking clot into a tubular catheter member, severing the drawn-in clot material and supplying fluid to remove severed thrombus from the tubular member. A fluid flow path with saline irrigation may be set up internal and external to the device to decrease the chance of device clogging. In addition, the method disclosed in Willard includes a step where fluid is introduced into the vessel in order to dilute the thrombus and modify its consistency. Diluting fluid is fed to the clot in the vascular system through a hole in the catheter or between the catheter and a surrounding sheath. The need to perform these additional maneuvers and the device design illustrate the as-yet unsolved limitations even with recently proposed clot removal technology. For example, the introduction of fluid into a clotted vascular space is not desirable and possibly contraindicated in many clinical circumstances. Certainly in the ideal thrombectomy device, fluid infusion into the vessel lumen, or any other clot modification maneuvers should be unnecessary to accomplish clot removal.
As described, these previous devices collectively suffer one or more deficiencies including cost, mechanical complexity, large cross sectional diameter secondary to multiple channels and septa between the channels. In addition, embolization of clot and other safety concerns exist especially considering that significant amounts of energy must be transferred into the body, in order to accomplish clot modification. Because of these limitations, the search for the ideal thrombectomy device is still continuing.
It is to be noted that similar cutting instrumentation has been disclosed for use in atherectomy procedures. While these devices may appear to be similar to thrombectomy devices, atherectomy devices have not been used and are not generally applicable for use in thrombectomy procedures where the technical challenge is high volume clot removal and not the cutting of soft gelatinous clot. In atherectomy devices, the precise cutting of hard calcified and usually irregular and eccentric vessel-wall lesions is necessary under precise operator control, such that an exact amount of tissue is removed yet vessel perforation does not occur. The volume of removed substance is generally small and does not present a waste removal problem under most circumstances. Indeed the Simpson atherectomy catheter, which is the most commonly used atherectomy catheter in clinical use, has no waste removal capabilities and all debris is stored in the catheter tip, which may only be cleaned after the catheter is removed from the body.
Notwithstanding this basic difference in purpose between atherectomy and thrombectomy devices, multiple atherectomy catheters with irrigation channels to aid in debris removal exist. U.S. Pat. No. 4,846,192 to MacDonald is illustrative of this group. It describes a rearwardly acting surgical catheter. A centrally located drive shaft supplies irrigation fluid to the area of the cutting element via two opposing openings in the shaft. The design of this and other similarly functioning catheters that contain irrigation channels is such that tissue is cut into a small particulate size and fluid acts as a lubricant and as a carrier medium for the excised tissue to be washed away. Inspection of the mechanical characteristics and irrigation channel configuration of the MacDonald, Willard and other devices with similar capabilities will conclusively show that they are not designed for the repetitive and intentional clogging as a mechanism for debris removal nor can they generally tolerate such an occurrence without seriously impacting their performance. Indeed this occurrence must be avoided since a full obstruction of the catheter lumen suction channel and/or cutting chambers, would not be completely cleared via irrigation through their respective irrigation channels.